Topic 9
1. The organization of aircraft towing
2. Starting process of aviation engines
Electric systems of start.
Air system of the engine start.

Aircraft towage. Starting process of aviation engines. (Topic 9)

1. Topic 9

Aircraft towage. Starting
process of aviation engines.

2. 1. The organization of aircraft towing

For good safety movement of the attendants on platform
and parking, economy of a resource of aviation
engines and aviation fuel, and also protection of an
environment against noise and pollution instead of
taxiing the plane its towing is applied. However, towing
increases aircraft staying in the airports that has an
airtransportations which is the basic parameter
describing efficiency of planes usage.
The increase in commercial speed increases flying time
by one plane, accelerates delivery of passengers,
mails, cargoes, etc. Hence, all positive parts
connected to towing are necessary to use with the


Tractors as a rule are applied to towing of airplanes. On a
way of aircraft towing tractors with towing adaptations,
devices with a friction gear and with use of weight of the
plane are applied.
The greatest distribution was found simple and reliable
ways of aircraft towing with the help of machines - tractors
which transfer drag force on the plane by means of tow bars
- at movement of an aircraft by «forebody forward" and with
use two sling of identical length at movement of an aircraft
by «a tail unit forward».
Schopf aircraft towbar tug.


The tow bar has the coupling device with a forward rack
of the chassis of the plane and a towing hook of the
tractor. Thus it is carried out rigid coupling of the tractor
with plane and transfer of drag force. At towing of an
aircraft by «a tail unit forward» one end of everyone
slings joins in special unit to racks of the basic chassis,
and the second ends with the help of towing link are
attached to a hook of the tractor. For improvement of
maneuvering in this case, it is used manual carrier of a
control which is attached with the help of pins to the
forward rack of the chassis.


Recently universal carrier has found application, which
has simplified process of towing. The light transitive
crutches are jointed to forward rack of an aircraft. The
complete set for different planes is transported in the
tractor. They are connected also to the common for all
planes carrier. It provides constant readiness of the
tractor for towing of various types of airplanes. Now air
field tractors such as БелАЗ-6411, БелАЗ-7421 КрАЗ256 are applied. They are equipped with universal
carriers and complete sets of transitive crutches.


The flight intercommunication is used for
coordination of action of the tractor driver with
the pilot or technician, carrying out control of
an aircraft at towing.
Tractors should operate reliably at speeds of
movement of 5 km/h and develop sufficient
drag force on a hook. For reduction of
wheelspin of the tractor the ballast is loaded
into its body at the moment of breakaway from
a place, the chain is put on wheels and sand
blaster is mounted at each wheel.


Towing of the plane with the help of a friction gear
has a number of advantages, namely: absence of
a connecting link - carrier; small radius of turn of
the plane at maneuvering; smooth breakaway of
the plane from a place and soft braking. But these
advantages are fair only at a dry air field covering
that limits application of the given method.
The principle of action of the frictional device for
towing the plane consists in transfer from it on a
forward wheel of the plane chassis of the torque,
sufficient for breakaway and movements of the
plane. Such devices are applied, basically, for
towing of light planes; they have found wide
application abroad.


At towing of an aircraft it is necessary to observe the
following rules:
towing of an aircraft is necessary to provide according to
the operating instruction of the given type of the plane;
strictly carry out commands of responsible for towing
which should be in sight the driver of the tractor and the
person who are taking place in a cabin of the plane;
drivers of the tractors trained to the towing rules of
corresponding types of planes are admitted to towing of
an aircraft;
the tractors used for towing, should be equipped with
means of radio communication, dimensional and
flashing fires;
speed of towing should correspond to the instruction on
towing of given type of plane;
Towing should be carried out without jerks and sharp
turns, breakaway and stop is made smoothly.

9. 2. Starting process of aviation engines

Aviation gas turbine engines and piston engines
do not possess the starting moment. Their start
needs preliminary rotation of a rotor up to the
certain frequency of rotation providing reliable
submission, ignition of fuel and an output of the
engine on an idle mode.
Process of preliminary rotation of a rotor of the
aviation engine up to the set frequency of rotation
(small gas) is called start of the engine. All
operations of start and its control are automated.
As ground means of automation of power supplies
for start of aircraft engines electric and pneumatic
devices are used.

10. Electric systems of start.

There are three basic types of electric starter start of
aircraft engines: direct, step and smooth. They differ
among themselves on character of change of a voltage
and consumed by an electrostarter current during start.
The direct start is such start, during which the value of a
supply voltage 24 V (28,5 V) of an electrostarter for
whole cycle of start of an aircraft engine remains almost
constant. Direct start is applied to aircraft engines which
during start are consumed a small amount of the
electric power.
As power supplies at direct start direct current
generators, rectifiers with a voltage 28,5 V and storage
batteries with a voltage 24 V are applied.


Step start is such start, during which the initial supply
voltage of an electrostarter through the certain time
interval is doubled (for example, from 24 V to 48 V) due to
series connection of two independent current sources by
their switching during start from parallel connection on
series. Such system of start is called «System of start
24/48 V». It increases reliability of engine start, excludes
sharp dynamic loadings on the coupling mechanism of a
starter, raises efficiency of energy use of power supplies.
Smooth start is such start during which the value of a
voltage supply of an electrostarter of an aircraft engine
changes smoothly from 0 up to 70 V. Smooth start
excludes occurrence of dynamic loadings in kinematics of
an aircraft engine, provides an optimum mode of start, and
reduces charges of the electric power. This system finds
application at start of aircraft engines of heavy planes at
which capacity of a starter makes some tens kilowatt.


One of the basic sources of power supplies for
airplanes are air field mobile electrounits of
types: АПА-352МУ, АПА-50, АПА-35/30, АПА5Д, АПА-100, etc., mounted on the chassis of
the automobiles.


All modern airports receive the electric power from
industrial three-phase alternating-current mains
with voltage 380 V and frequency of 50 Hz.
However this electric power is not suitable for a
supply of onboard systems of airplanes. For
transformation of the industrial electric power to
the necessary electric power for aircrafts rectifiers
and converters are used which can be stationary
(СК-60, СК-100) and mobile (АВП-20У1, АВ-2Ф,
АМГА-17, АМГЭ-60/30М).


At operation of power supply systems of an aircraft it is
necessary to observe the following key rules of the
safety precautions:
to be convinced, that all switches in cabins of the plane
are in the neutral or switched off position at connection
of aircraft to a source of power supply;
to be convinced in value of a necessary voltage after
connection to an onboard network of a ground source of
the electric power;
to make correct switching on of the control units,
stipulated only for a set operating mode;
all additional loadings, including plane units are
disconnected at engine start;
to connect corresponding cable connections at start on
system «24/48 V»;
to eexclude application of fuses;
to supervise a degree charging storage batteries.

15. Air system of the engine start.

The air system of start is
applied on airplanes with
powerful engines. They
also can be onboard and
In ground air systems of start the compressed air from a
ground source on a hose moves on an air starter which
represents the air turbine with the big frequency of
rotation. This turbine starter with the help of a reducer is
connected to shaft of an aircraft engine and provided its
rotation up to necessary frequency. Air starters are
posses by smaller weight in comparison with
electrostarters of identical capacity.


As onboard sources of compressed air auxiliary power-plants (APP)
are used. And ground installations of air start are applied to
preservation flight resource APP such as УВЗ-2, etc. УВЗ-2 is a
source of power supplies of onboard systems of the plane except for
reception and submission of compressed air on rotation of an aircraft
engine. УВЗ-2 units are mounted on the chassis of automobile УАЗ452 and include gas turbine engine ТА-6А, generators of constant
and an alternating current.
At operation with УВЗ-2 it is necessary
to observe the following safety
precautions rules:
it is necessary to supervise
serviceability of its fire-fighting system
before the beginning of operation with
it is forbidden to make refuelling of an
aircraft at working engine УВЗ;
hose of УВЗ should not have sharp
excesses and twisting, damages of a
to watch fastening of a hose to onboard
union of an aircraft.
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